Internal combustion engines generally have one or more camshafts, which drives/drive gas exchange valves in the internal combustion engine, or possibly a high-pressure pump in a fuel feed device. On the camshaft are cam formations, which bear on the gas exchange valves and thereby determine the time-trace of the valve lift for the gas exchange valves. The camshaft is linked to the crankshaft by means of a transmission, which generally includes gears and a chain.
The phase position of the camshaft relative to the crankshaft has a critical effect on the combustion process in the cylinders of the internal combustion engine, and hence also on the exhaust gases generated by the internal combustion engine. Thus, the quantity of fluid flowing in for each working cycle of a cylinder depends on the phase position of the camshaft relative to the crankshaft. This means that a precise knowledge of the phase position of the camshaft relative to the crankshaft is a prerequisite for a precise determination of the mass of fuel to be dosed into the combustion chambers, and possibly for the selection of the ignition timing.
Internal combustion engines have a crankshaft angle sensor, which detects the angle of the crankshaft. In addition, internal combustion engines regularly have a camshaft angle sensor which detects the angle of the camshaft. From the crankshaft angle which is detected and the camshaft angle which is detected, it is possible to determine the phase position of the internal combustion engine. However, faulty arrangement of the camshaft angle sensor or other camshaft sensor faults can lead to an incorrect determination of the phase position.
DE 196 38 010 A1 discloses a method for determining the angular position of a crankshaft within a working cycle of an internal combustion engine. For this purpose, the output signal from an intake pipe pressure sensor is evaluated during the time when a reference mark on the crankshaft is present. Then, depending on the output signal, an assignment is made indicating whether the crankshaft is within the first rotation of the working cycle concerned or the second. In doing so, use is made of the fact that the time-trace of the intake pipe pressure in the first rotation differs in a characteristic way from its time-traces in the second rotation of the crankshaft.
DE 101 16 485 A1 discloses that it is possible to reconstruct a camshaft signal by computation from the intake pipe pressure detected by a pressure sensor.
U.S. Pat. No. 5,495,830 A discloses, for an internal combustion engine with variable phase positioning, a method for determining the phase position of the inlet valve relative to a piston, by reference to a crankshaft angle. This determines the point in time at which the piston is positioned at a prescribed crankshaft angle, so that there is a known air intake volume in the cylinder. At this point in time, the pressure in an air induction pipe, between the intake valve and a throttle valve, is determined. Further, while the inlet valve is
closed, the pressure in the induction pipe is determined. The phase position of the inlet valve is determined from a predefined characteristic line, as a function of the pressure determined.
DE 101 47 835 A1 discloses a method for determining the effective valve lift curves for an internal combustion engine. This involves calculating a time-trace of the cylinder pressure synthetically, on the basis of prescribed values for the time-point of opening, the valve lift travel and the maximum valve lift for the valve, starting from the measured pressure value at the point in time when the exhaust valve opens. The synthetically calculated time-trace of the cylinder pressure is then compared with a measured time-trace of the cylinder pressure based on the cylinder pressure, the exhaust gas pressure and the intake pressure. The time-trace of the valve lift for which the difference is a minimum is determined by systematic changes to the prescribed values for the synthetically calculated time-trace of the valve lift, and by repeating the comparison between the measured time-trace of the cylinder pressure and the calculated time-trace.
Ever more stringent legal regulations on emissions make it necessary to detect the phase position of the camshaft relative to the crankshaft reliably and precisely.